| With the rapid development of peoples consumption demand for edible vegetable oil,the gap between domestic vegetable oil supply and demand is expanding.In China,rapeseed(Brassica napus L.)supplies about 5.2 million tons of high-quality edible oil annually,accounting for 47% of domestic vegetable oil.Thus,it is of great importance to improve the seed oil content of rapeseed.The lipid metabolism of Arabidopsis(Arabidopsis thaliana)has been annotated to 23 metabolic pathways.After aligning all the Arabidopsis lipid metabolism genes to rapeseed,approximately 2000 orthologs of lipid metabolism genes were annotated in the rapeseed genome.However,about one-third of the Arabidopsis genes remain to be functionally characterized,it can be expected that in rapeseed there are genes of the lipid metabolism pathway that are still awaiting functional annotation.Peanut(Arachis hypogaea L.),sesame(Sesamum indicum L)and rapeseed are important oilseed crops in China,but the average seed oil content of rapeseed cultivars is about 42%,which is around 10% lower than that in peanut(50-55%)and sesame(55%-58%).In order to select target genes related with high seed oil content from peanut and sesame for improving seed oil content of rapeseed,the comparative genomics and transcriptomic were used to reveal the gene copy number variation of lipid metabolism and to construct the lipid metabolism co-expression network in the three oilseed crops,respectively.Main results in this research are as follows:1.By aligning the three oilseed crop genomes with the Arabidopsis genome,the results showed that 87676,58107 and 23218 homology genes were identified in rapeseed,peanut and sesame,including 2659,1582 and 1051 lipid metabolism genes,respectively.Compared with Arabidopsis genes,6066,5590 and 5365 genes showed gene copy number expansion,including 233,214 and 195 lipid genes in rapeseed,peanut and sesame,respectively.Among the 23 lipid metabolism pathways,except for Mito Lipopolsach and Cutin II,the remaining21 pathways showed expension in the three oilseed crops compared with Arabidopsis,from which gene of 20 pathways had higher expension fold in peanut and sesame than rapeseed,such as genes involved in Fatty acid synthesis,Fatty acid elongation and Triacylglycerol biosynthesis pathways.2.To reveal the differences of lipid metabolism pathways among the three oilseed crops at the transcriptional level,we phenotyped the seed oil content of 71 rapeseed lines,49 peanut accessions and 100 sesame accessions,and performed the RNA-seq using young silique tissues per lines.The average seed oil content were 36%,50% and 52% in rapeseed,peanut and sesame,respectively.Differentially expressed genes(DEGs)detection was carried out between 10% extremely high and low seed oil content lines in each crop,then 3757,2466 and 927 DEGs were detected in rapeseed,peanut and sesame,respectively.3.We aimed to select target genes related with seed oil content from peanut and sesame,we performed co-expression network analysis by using lipid homologous genes as “bait” to“fish” DEGs in each crop.Thus,1886,630 and 730 DEGs were further selected.The enrichment analysis were carried out for the genes in the lipid metabolism co-expression network of each crop,respectively.The results showed that three crops were commonly enriched in lipid metabolism related pathways,such as fatty acid synthesis,lipid transport and lipid biosynthesis.Besides,we also found that genes in rapeseed were specifically enriched in response to heat and glucosinolate metabolism,genes in peanut were specifically enriched in glycolysis and pyruvate metabolism,genes in sesame were specifically involved in glycerol-3-phosphate metabolic process,response to gibberellin,seed coat development,long-chain fatty acid transport,lipid homeostasis,and phosphatidylethanolamine biosynthesis process.The commom enrichment pathways between peanut and sesame were phosphatidylcholine metabolism,CDP-DAG synthesis and acetyl-Co A metabolism.4.To screen candidate genes,we mainly focused on 150 genes only existed in the lipid co-expression network of peanut and sesame.These genes comprised of 113 lipid genes and37 novel genes.One candidate encoding WRKY6 from the 37 genes was select that each crop had one paralog in the co-expression network and co-expressed with 8 and 100 lipid genes in peanut and sesame,respectively.The expansion fold change in peanut(2.75)and sesame(2.50)were much higher than that in rapeseed(0.60).Besides,two and one paralogs showed differentely expressed in the extremely lines that high seed oil content lines had significantly lower gene expression,in according with the previous result that knock-out mutant of WRKY6 showed higher seed oil content. |
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